Flex constantly tracks your day-to-day activities, including steps, distance, calories burned and active minutes: at night, it monitors your sleep quality and duration. The tracker fits into a comfortable silicone band that is soft-touch and water-resistant. A row of 5 white LED lights shows your progress. It also has a silent wake alarm that gently vibrates to wake you. The interface is entirely managed by the app, and all data are automatically transferred via Bluetooth 4.0 technology.. Material:Plastic